This invention relates to the transmission of binary data signals and in particular, to the conversion of a low speed binary data signal to a higher speed line transmission rate.
With the standardization of the United States of the T1-type pulse code modulation (PCM) system, a natural data transmission channel became available. The standard channel of such PCM systems accommodates 64 kbps. As a practical matter, the full capacity of the channel could not be employed for the transmission of data as other housekeeping chores would be necessary, and these would take up some of the capacity of the channel. Thus it was standardized on a 56 kbps transmission rate for data that would be applied to the standard PCM T1-type channel.
In order to make use of this available compacity it was necessary to permit subrates of the 56 kpbs capacity for data transmission. These were standardized at 2,400; 4,800; 9,600; and 19,200 bps. Because of the necessity to maintain the line transmission rate, it has become necessary to convert each of the standardized rates into a line transmission signal having a 56 kbps rate that can be accommodated by the telephone network.